Category Archive
‘Project HMX’: 108 Posts

As I mentioned in the Boom Stick post, I wanted to further isolate the air intake from the hot underhood air with an enclosure of some sort. After spending some time looking for inspiration under the hoods of modern muscle cars with aftermarket cold air intake systems, I figured I could build something similar myself.

As with any fabrication project, I started with a template. In this case, I cut up some boxboard and taped it together in different configurations before I settled on one that I liked. I then transferred that boxboard template to a craft paper template, mocked up the latter as a sort of dry run to figure out where to make cuts and the step-by-step process, then transferred the craft paper template to aluminum. As for how the air would come into the airbox, I initially thought I’d just use the air that slipped around the side of the radiator – there’s several openings in that area that would permit airflow – but for the sake of a less convoluted airbox design, I went with another option.

Without a front bumper, I have two large holes in my front valance. With a short length of three-inch dryer duct, I can then connect one of those valance holes to a hole I drilled in the inner fender, which will serve as the bottom of the air box. Right now the ductwork is rather inelegantly secured with a hose clamp on one end and nothing on the other end. I’ll eventually fabricate cleaner attachments, but these work for now.

Cut, fold, rivet, and the airbox takes shape. I’m not entirely happy with the sheetmetal screws for the lid, but they work.

Test fitting it allowed me to tweak the shape before cutting the hole for the Boom Stick to pass through. Because of the compound angles, I ended up eyeballing the pass through more than I actually measured it, and thus cut the hole a little oversized. I figure some door edge guard will fill the gap.

I had some Dynaliner left over from when I redid the car’s interior, so I took the same craft paper template, cut it up into its individual components, and used those for templates for the Dynaliner to go on the inside of the airbox. At the same time I painted the airbox with black high-heat paint. The combination of the paint and the Dynaliner should further insulate the box from the underhood temperatures.

As you can see above and at the top of this post, I also painted the Boom Stick (instead of regular primer, I laid down an initial coat of paint formulated to adhere to plastics before I hit it with the grill paint). I should probably borrow an infrared thermometer or remote temperature sensor to test the efficiency of the airbox, but that’s fancy pants talk right there. The butt dyno says it works, so I’m happy with it.

Along with fine-tuning the stroker, I’ve also lately been focusing on refining the installation of the engine into the Spirit AMX body. When I originally installed it and got it running, I threw together a quickie air intake setup that got the job done, but had its drawbacks.

All I really did was cut a section from the donor Jeep Cherokee’s airbox to get the fitting for the front CCV hose and just long enough to fit a K&N cone air filter to the stock elbow. But as you can see in the lead image, that puts the air filter almost right atop the header and all its heat and it sandwiches the filter between the power steering pump and the computer – not the ideal location, but I wasn’t sure where else I could stick it.

I knew even before I’d started this project that the stock Chrysler EFI system from the 4.0L HO Jeep six-cylinder would need some tweaking to work with my 4.6L stroked six. Increasing displacement meant I’d need more fuel. More fuel meant I’d need more air, and more of both meant I’d need a way to convince the stock computer to play along, or else driveability, economy and power would all three suffer.

First, I started with 24 lb/hr blue-top Ford 5.0L V-8 fuel injectors from FiveOMotorsport. Some stroker builders have reported that they’ve been able to get their stock 19 lb/hr injectors to work, but the math shows that the stock injectors would be at their maximum duty cycle supplying a stroker, so I went with the Ford injectors to be on the safe side. While the injectors worked with the stock Jeep fuel pressure regulator (fixed at about 37 PSI), I still encountered lean-outs with that setup, so I decided it was time to step up the pressure to the 49 PSI the Ford injectors were meant to run at.

HESCO appears to be the only company offering an adjustable FPR for the 4.0L Jeep six-cylinder, and as you can see from the above photos, it’s significantly larger in both girth and length than the stock FPR. Length isn’t an issue, but the FPR hold-down bracket is the exact diameter of the stock FPR, so I had to hit it with a Dremel to open it up to the HESCO FPR’s diameter. After that, adjusting the fuel pressure is simply a matter of installing my fuel pressure gauge, starting the engine, loosening the jam nut and then turning the stalk with a slotted screwdriver (all the time with the vacuum line disconnected). Once I got it to 49 PSI, I cinched the jam nut and reconnected the vacuum line.

That seemed to cure the lean-outs (at least, the computer stopped throwing the code for lean-outs), but I wanted to be sure, and I still wanted finer control over how much fuel the EFI system provided the engine. Chrysler’s OBD I system, however, isn’t easily tuned; one can’t just add a performance chip to it or plug in an OBD II-style reader to fiddle with the fuel maps. There’s at least a couple piggyback computers for the 4.0L out there, and I’ve considered replacing the OBD I system with MegaSquirt, but I didn’t want to drop a few hundred dollars on a piggyback or go through the effort of rewiring this engine again.

Thus my two-part approach. First, it makes little sense to start down the road of fine-tuning an engine with a narrowband oxygen sensor, so I bought a wideband sensor and PLX M-300 controller off of Steve Berry after he decided not to use them for his MegaSquirted Volvo 1800 project. Fortunately, the controller included a narrowband emulator, allowing the wideband sensor to still send a signal to the computer, along with an output for a datalogger. I would have liked to run an air/fuel ratio gauge, but the seven-segment display will do for now.

The wideband sensor plugs directly into the controller, which in turn needs only a 12-volt power signal, ground, and a wire over which it can send the narrowband signal. I figured I could use the stock oxygen sensor wiring harness to provide those three things – three of its four wires already served those functions anyway – but I didn’t want to make permanent splices into the harness, in case I ever wanted to easily switch back to the narrowband sensor. So I dug through my junk pile and found another narrowband sensor – one that I’d replaced when I first built the engine – cut the connector from it, and spliced the wideband controller’s wires into the connector. A couple trial-and-error runs and I got the wideband sensor working and talking with the computer, so I tidied up the wires and ran them through an unused grommet in the firewall so I could keep tabs on the AFR from inside the car.

The wideband itself doesn’t allow me to control the AFR, but my MAP sensor voltage adjuster does. Even though I’ve already gone through a couple different iterations of the MAP voltage adjuster, both of which worked just fine, I decided to do up another to work with my glovebox-mounted control panel. Of course, that meant installing the panel as well, something I’d never gotten around to after I fabricated the panel late last year. On this third version of the MAP voltage adjuster, I added a couple ports so I could plug in a multimeter while setting the MAP voltage. Less voltage leans out the mixture, while more richens it. Stock is 5.15 volts, and I’ve found that a setting of 5.35 volts keeps the AFR right around stoich and so far returns about 22.5 MPG, but I’m still experimenting with the voltage setting.

I don’t have complete control over the fuel maps with this setup – it would take a far more sophisticated setup to do that – but I can at least get it close enough for daily driving. Bonus: It’s now set up for dyno tuning, should I get a chance to do that.

When I first brought out Project HMX after its winter slumber, I noted some brake issues – they felt soft and would lock up when I really jumped on them. But under normal braking, they seemed passable. Maybe the brake fluid in the lines had just absorbed some moisture while the car sat over the winter, I thought, so I bled the brakes all around and took it for another test drive. Still soft. Bled again, still soft. What’s going on here?

What I neglected to do while bleeding the brakes was to perform a visual inspection of the entire brake system. Had I done that, I would have seen the paint peeling from the spindle uprights in the front suspension, a clear sign of a brake fluid leak, and saved myself some time and effort (and about half a bottle of brake fluid).

As you can see from the photo above, the front brake hoses pass behind the upright forward to the caliper. The drop plates that I installed over the winter, of course, added about an inch to the front track of the car by pushing out the spindle, the caliper bracket and the caliper itself a half-inch per side, and at the time I believed the brake hoses had plenty of clearance to make the straight shot into the caliper. As it turned out, however, the uprights ended up interfering very slightly with the brake hoses, causing it to leak. It didn’t leak much, but enough to cause the issues I’d been having.

Here you see the end of the brake hose where it would leak – right at the swivel joint – along with the adapter to mate the aftermarket stainless steel brake lines to the calipers. At this point, I could have just removed the drop plates and solved the problem, but I didn’t want all that effort to go for nothing, so I started to look for ways I could get the brake hoses to clear the uprights. Modifications got me into this problem, maybe modifications would get me out of it.

Indeed they would. Some perusing of the Russell Performance catalog turned up these 90-degree banjo fittings with the correct 3/8″-24 fitting for the caliper and -3AN fitting for the braided stainless steel brake hoses.

As far as hardware goes, they’re pricey, but they did the job, neatly routing the hoses away from the uprights. I replaced the hoses while I was at it (not shown in these photos) just to be double sure I’d have no more leaks. Spent some time afterward confusing opposing traffic by standing on the brakes, and it all seems to work as it should now.

Several readers have wondered lately where I’m at with Project HMX, and I can’t say I’ve made much progress lately. In fact, since dropping the front end a couple inches back in December, pretty much all I’ve done is take it off the battery charger, change fluids and start it up for the season. I did make an effort to clear my schedule recently to take it out for a spin and grab a few photos of its new stance, much better compared to what it looked like almost a year ago.

It ran strong, as expected, but that’s not to say it ran perfectly. It stumbled on partial throttle, the brakes felt soft and locked up on me in hard stops, and the computer threw some puzzling codes halfway through the trip. Hopefully, I can get at least the first two issues resolved before the AMO National this July in Boston.

Right at the top of my to-do list while driving Project HMX around this past summer was getting the front end to sit a little lower. Taking all sorts of weight off the nose of the car led to its taildragger stance, as seen above back in May. The car handled just fine, especially after getting it aligned, but the stance was what everybody noticed first, leading them all to ask whether it was an Eagle. Plus, the reverse rake made it tough to adjust the mirrors properly.

From some eyeballing, it appeared that the front and rear fender lips on this car were supposed to be level, so I went around the car taking careful measurements to establish just how much I needed to drop the front end. I measured not just from the ground to the fender lip, but also from the hubs to the fender lip to try to eliminate as many variables as possible and establish the true ride height of the car. According to my measurements, the front end sat right around 1-3/4 inches higher than the rear.

With the HMX back on the road, I’ve put in way more seat time than wrench time on it this past summer, but that didn’t mean I wasn’t keeping an eye out for ways to improve the car’s driving experience. Since restoring the interior, I’d hardly touched it, but I knew I wanted some sort of control panel for the MAP voltage adjuster, an adjustable thermostat for the electric fans and a couple other goodies. Considering I wouldn’t be using these knobs and switches all the time – and that I had some unused space in the glovebox – I decided to house them all in there. It was only with the recent onset of colder weather and the ceremonial putting the car up for winter did I take the time to fabricate the control panel.

Here’s what I had to start with. I initially considered a blanking plate for the radio (the hole for which is on the far left of the above photo), but could never come up with a configuration I liked that fit the space. Instead, the glovebox interior offered a blank canvas with a bonus of an existing hole through which I can pass wiring.

First step was to create a paper template. This is actually the fifth or sixth iteration of the template, after adjusting dimensions and changing my mind on configurations. Not visible here is a flange on the front piece that will allow me to screw it to the side of the glovebox – to access those screws, I had to make this a two-piece design. When making templates, make sure to mark them up with notes so you don’t confuse the orientation with the templates out of the car.

Transfered the template to aluminum. Note that even this far along, I was still making adjustments to the templates before applying the dimensions to metal.

I don’t have a brake, so I MacGyvered one out of a straightedge, the edge of my workbench and a pair of clamps. Carefully line it up and bend it as evenly as possible as close to the bend point as possible.

Turned out halfway decent. Note that I rounded the sharp angles. Got fed up with slicing and dicing my fingers. I drilled the two holes on the top flange to correspond with existing holes in the glovebox for a remote hatch popper that never worked right.

Along with the second piece, I cut out some paper representations the same sizes as the knobs and switches I plan to install in the panel. That way I can refine my ideas on where exactly to place them before drilling holes. Still have a couple holes to drill to mate the two pieces. Also, I haven’t yet figured out how I’m going to finish it – leaning toward a black wrinkle finish, but brushing the aluminum would match the dash inserts nicely. In the lead photo, you can see how nicely the two pieces fit when mocked up in the glove box; I only had to trim each piece a little to get them in place.

One thing that’s bothered me ever since I first built the stroker 4.6L engine for Project HMX was the serpentine belt routing. Recall that I got the engine out of a 1993 Jeep Cherokee and that I’ve decided to forgo air conditioning, along with any sort of mechanical fan. I’ve also installed a 1999-up Grand Cherokee power steering pump and idler pulley and I’ve had to reroute the belt slightly to accommodate the Advance Adapters relocated crank position sensor. At the time, the best solution I could come up with used a grand total of four idler pulleys (two traditional idler pulleys and two pulleys reduced to serving as locators for belt routing) and a belt about as long as a Burmese python. Still, it worked.

Not until I bought my 1994 Grand Cherokee, however, did I realize I could have severely simplified the serpentine belt setup. You see, XJs and ZJs might use the same 4.0L engine, but the brackets on the passenger side differ between the two. I believe this was a packaging decision on the Jeep engine designers’ part: The XJ has a lower hood and grille, and uses a smaller offset mechanical fan (augmented with an auxiliary electric fan) versus the ZJ’s larger, traditionally mounted mechanical fan, so the XJ had to reposition the alternator way down low to make room. Thus I found a guy parting out a ZJ’s 4.0L and bought the alternator and air conditioning brackets off him.

With a little sandblasting by Litwin and some aluminum paint, they looked about as good as new. Interestingly, the two brackets weighed almost nothing, and I see an “Mg” cast into one of them. Magnesium?

Swapping the two took a couple hours, and the difference became immediately obvious. With the alternator repositioned higher in the engine bay, I could eliminate two pulleys (the one formerly used to spin the XJ mechanical fan and the dummy taking the place of the air-conditioner pulley) and run a much shorter belt. Here’s a couple before-and-afters showing the new alternator location from above and below:

While disassembling the XJ brackets, I found a film of rubber dust in one area where the belt came too close to a bolt on the timing cover. I believe that’s what was causing a minor, but irritating and persistent, squeal from the front of the engine, so chalk up another good reason to swap the brackets. With it all bolted back together and the right belt in place (using the string method shown in the lead photo), the squeal went away. It’s possible I freed up a little more power with the swap – and it certainly can’t hurt to get the alternator away from water spray and road debris – but I think the real benefit here comes from simplifying the accessory system, making belt changes easier and reducing the number of failure points by two.

Finally, as it looks now. I may have to relocate some things now to take advantage of that unoccupied flat spot. Suggestions?

Good news for those of you waiting patiently (verrry patiently) for an update on Project HMX: It’s out of the garage and back on the road. Over the weekend I slapped the exhaust back on it, dropped a fresh battery in it and the stroked 4.0L barked to life like it was just running the day before. Took it into town for an alignment yesterday, using the specs from Performance American Style (thanks, Marc Montoni, for pointing those out!), and now it handles like a dream. In fact, it’s already literally tearing up the pavement, as you can see from the photo above.

Still have a stumble I have to figure out, and a whole list of other minor squeaks, rattles, and other annoyances, but at least it’s running. My plan is to spend this summer driving it and ironing out all those imperfections, then save up my nickles and dimes for paint.

It’s funny how you can lose inertia on a project in the blink of an eye. I hadn’t intended to let Project HMX sit for about a year with nothing doing on it – in fact, I had sworn to myself that I’d constantly do something, anything, on it to keep my momentum going – but all the other projects, minor crises, family events, and plain ol’ need for downtime that make up a normal life kept me away from the car since October. Plus, I was also not looking forward to the rear axle and suspension swap that I knew would be next.

Quick recap: The axle under the car belonged to a 1982 Spirit GT with weak 2.35 gears and small 9-inch brakes. The axle I spent last autumn cleaning up came from a 1979 AMX with weak, but marginally better, 2.53 gears and much better 10-inch brakes. I also had the stiffer springs and larger 3/4-inch rear anti-roll bar from the same 1979 AMX which I intended on swapping into Project HMX at the same time as I swapped the axles.

So I started by disconnecting the driveshaft and brakes and removing the GT springs and axle, as you can see above. Not too difficult once I busted through the rust. I’d already removed the old shocks and anti-roll bar end links some months ago.

Service manual said to bolt up the shackles to the bracket at the rear, then move forward to insert the bolt through the front spring eye. Service manual made it sound rather easy-peasy.

Instead, the front spring eye came nowhere close to the forward mount (upper right corner of the photo), no matter how much cajoling and prying I tried.

Solution? Spring spreader. O’Clair recommended it and let me borrow the one we’ve used on the Hemmings Speedster. This particular spring spreader was made specifically for Model A/Model T springs, so I had to adapt it to these AMC springs with a fan spacer. Once I figured it all out for the first spring, it didn’t take more than 15 minutes to do the second spring.

I still have to install the new shocks and anti-roll bar end links and reconnect all the brakes, but I just had to throw the wheels and tires on to finally see it sitting at the proper ride height rather than with a droopy rear end, as it sat before. Once I get this all buttoned up, the next big task will be the bodywork. Joy.